<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <style>
    body {
      background-color: gray;
    }

    .big {
      width: 400px;
      height: 400px;
      background-color: pink;
    }

    .small {
      width: 100px;
      height: 100px;
      background-color: red;
      border-radius: 50%;
      overflow-wrap: break-word;
    }
  </style>

  <body>
    <div class="big">
      <div class="small">
        ddddddddddddddddddddddddddddddddddddddddddd
      </div>
    </div>
  </body>
</body>

</html>